1.6.11 problem

[ZiNgA BuRgA]

Please do not go about randomly deleting lines of code or files.  They are there for very specific reasons and modifying things without knowing what they do can cause greater problems.

64MB is quite a lot of memory to use for a script, and it's there for good reason.  In other words, you shouldn't be raising the limit.
Look at the debug stats that MyBB prints out at the bottom of each page.  On various pages, what's the memory usage?  Try with XThreads enabled and disabled.  This should give you an idea of whether it's causing the memory issues.